The invention relates to an apparatus for converting cinematographic pictures into video signals, which apparatus comprises a film gate, transport means for moving a film through the film gate, and opto-electronic means for scanning a film frame, which is located in the film gate, with a light beam and for converting the light beam which has been modulated by the film frame into electrical signals.
Such apparatus is known, inter alia from the article: "Vom Super 8 Film auf den Farbbildschirm" in: "Funkschau" 1974, No. 9, pages 956-962. In the known apparatus a film frame is scanned with a light beam obtained from a cathode ray tube. The light beam transmitted by the film is received by, in principle, a single radiation sensitive detector, for example in the form of a photomultiplier. The detector supplies an electronic signal which, after processing in electronic circuits, can be displayed by means of a conventional television set.
For reproducing a colour film with a colour television set, a colour splitting system, for example comprising dichroic mirrors, may be disposed in the radiation path of the light beam coming from the film. Said system splits the light into a red, a green and a blue beam, which beams propagate in different directions. Each of the three radiation paths thus formed includes a radiation sensitive detector.
In the cathode ray tube a rectangular area of the picture screen is scanned by an electron beam. This area, which has a uniform brightness, is imaged onto a film frame by an objective. Thus, all points of a film frame are sequentially imaged on the detector, or on the three detectors.
The use of a cathode ray tube in apparatus for converting cinematographic pictures into video signals has some drawbacks, especially if said apparatus is intended as a consumer product. The cathode ray tube must be operated at high voltages in order to obtain a satisfactory brightness. As a result of this the picture screen of the cathode ray tube will emit a comparatively large amount of X-radiation. As always at least one complete film frame is to be imaged, stringent requirements must be imposed on the optical system which is used. Furthermore, steps must be taken to compensate for the attenuation of the marginal rays relative to the central rays of the beams and to compensate for the persistence of the c.r.t. screen.